Post-menopausal women have a poorer prognosis after myocardial infarction (MI) than men. Partial explanations for the greater mortality and morbidity in women are loss of beneficial effects of estrogen or gender differences in age, coincident diseases, or treatments. Minimal attention has been given to the plausible alternative explanation that gender influences the basic pathophysiological outcomes of MI, specifically outcomes affected by the cardiac antioxidant defense systems (ADS). ADS provides vital protection against the reactive oxygen species (ROS) that are released during the detrimental ischemia and reperfusion (I/R) events of MI. Mitochondria are a dominant target site of ROS leaked in small amount during normal oxidative phosphorylation and in massive amounts during I/R. Mitochondrial ADS has been reported decreased in the hearts of male rodents by aging. My preliminary research indicates that aging has little effect on cardiac mitochondrial ADS of female rats, and thus provides strong evidence of gender differences in responses of cardiac ADS to aging. Proposed research will test the hypothesis that gender, age and disease are interdependent variables in the vulnerability of cardiac mitochondria to injury by ROS. Hyperthyroidism is the disease for study since it is reported to increase oxidative stress from ROS leakage in association with modified ADS status in cardiac mitochondria of male rats. Further research in my laboratory has indicated that the minimal effects of hyperthyroidism on cardiac mitochondria of female rats may be partially beneficial. AIM 1 will compare the effects of gender and aging On the responses of rat cardiac mitochondria to repeated short ROS insults followed by recovery periods. Experiments will expose cardiac mitochondria to a superoxide generating system and assess consequences of this insult on mitochondrial ADS, respiration, energy yield, and protein/lipid oxidation. AIM 2 will compare the responses of gender and aging on the responses of isolated perfused rat hearts to "stunning" produced by short periods of I/R. Then consequences of this insult on energy status, respiratory function, and indices of peroxidation will be monitored in mitochondria and cytosol. AIM 3 will evaluate the effect of chronic, elevated oxidative stress (e.g., hyperthyroidism) on rat mitochondrial ADS levels in heart, and on the responses of these mitochondria to repeated short ROS insults followed by recovery periods. Information obtained about correlations between ADS status and the vulnerability of cardiac mitochondria to ROS-mediated insults should provide clues to rationale development of better strategies for prevention/treatment of MI in women, especially aged women.